There exists a multilayer substrate that is formed by stacking and integrating a plurality of substrates. As an example of the multilayer substrate, Japanese Laid-open Patent Publication No. 2004-128029 discloses a multilayer substrate in which a high-frequency circuit component is mounted on a base substrate. Furthermore, Japanese Laid-open Patent Publication No. 2006-5097 discloses a multilayer substrate in which a plurality of thin-film multilayer circuits are formed on a base substrate.
When a substrate (a second substrate) that has a characteristic, such as a wiring density, that is different from a characteristic of another substrate (a first substrate) is stacked on the other substrate (the first substrate), there are cases in which an electric connection between the first substrate and the second substrate is realized on the surface of the second substrate that opposes the first substrate. When through vias are formed in the first substrate to enable connection in the direction of the plate thickness, wiring that electrically connects the first substrate and the second substrate is, in some cases, formed so as to bypass the through vias.